Processes for preparation of pectins are well known, as are many uses for these products. In general, typical pectin processes include the steps of:
(1) acid extraction from plant starting material at low pH, PA1 (2) purification of the liquid extract, and PA1 (3) isolation of the extracted pectin from the liquid. PA1 38.7 kg demineralized water PA1 9.9 kg 80% lsopropyl alcohol (IPA) PA1 0.66 kg CaCl.sub.2, 6 H.sub.2 O
In the acid extraction step, plant material is typically treated with dilute acids such as nitric-, sulfuric-, hydrochloric- or other inorganic or organic acids to remove the pectin from the cellulose components of the material. Commonly used plant starting materials are citrus peels from juice production and apple pomace from apple juice and cider production. Other plant starting materials can also be used, such as sugar beet, before or after sugar extraction, sunflower heads after removal of the seeds, and other vegetables or waste products from plants. Extraction conditions are selected such that a major part of the pectin molecules contained in the plant starting material is transferred from the cell walls of said plant starting material to the extraction medium.
The quantity and quality of the extracted pectin depends on the raw material source and the selection and control of the extraction conditions such as pH, temperature and extraction time.
After the acid extraction step, a mixture of solid plant material and liquid that contains the pectin remains. This mixture is then subjected to a purification step In which the solid plant material la removed by filtration, centrifugation or other conventional separation steps known to those skilled in the art.
The extract can, optionally, be further purified by ion exchange and concentrated by evaporation of part of the water. Alternatively, the purification step can be carried out by reverse osmosis, concentrating and purifying the extract in the same step.
The pectin in the acid extract can be isolated by reacting with aluminum salts after adjusting the pH. The aluminum pectinate gel thus formed is treated with alcohol/acid mixture to wash out the aluminum salt and transformed the pectin into pectic acid. The pectic acid can then be neutralized and a substantial amount of the water is removed by washing with slightly alkaline alcohol.
More commonly, the pectin is isolated by treating the pectin solution with an appropriate alcohol to render the pectin insoluble in the ensuing blend of alcohol and water. Any alcohol or other organic solvent miscible with water can be used, most often ethyl alcohol, methyl alcohol or isopropyl alcohol. isopropyl alcohol is most preferred.
The insolubilized pectin is separated from the alcohol/water mixture by appropriate means such as filtration, centrifugatlon, etc. The resulting pectin cake is dried and milled to the desired particle size.
in typical commercial processes, the presence of high levels of polyvalent cation is avoided in steps (1) and (2) as described above. While low levels of cation, i.e., those materials naturally present in the starting materials, may be tolerated in some instances, it has been the general practice to never add additional cation(s) to the processes. This would result in unacceptable increases in viscosity and unacceptable levels of insoluble pectin in the final product.
Industrially produced pectins are made up primarily of polygalacturonic acid chains in which rhamnose may be found. Neutral sugars may be attached to the rhamnose units. The anhydrogalacturonic acid makes up at least 65% of the dry matter in commercial type pectins. The galacturonic acids are partly esterified with methyl alcohol.
According to convention, pectins with more than 50% of the carboxylic acid groups esterified with methyl alcohol are referred to as high methoxyl pectins; whereas, pectins with less than 50% of the carboxylic acid groups esterified with methyl alcohol are called low methoxyl pectins.
The extract as obtained by the commercial production is composed of those molecules that are soluble under the conditions of pH, temperature, and time used during the extraction. The extract is composed of a mixture of molecules which differ according to molecular weight, distribution of molecular weight, and degree of esterification.
The properties of the pectin obtained are, therefore, very much dependent on the specific mixture of molecular configurations present in the isolated pectin. This mixture of molecules can be controlled only to a certain degree by the pectin manufacturer by selection of raw materials and extraction conditions. For this reason, variation in pectin properties is seen from extract to extract, from manufacturer to manufacturer, and normalization of the properties is generally necessary. This may be accomplished by blending different extracts and diluting with acceptable diluent such as sugar, dextrose, fructose, etc.
One of the main functional variations between high methoxyl pectins is their sensitivity to the presence of varying concentration of polyvalent cations. it is known that pectins of high degree of esterification, e.g., greater than fifty, are not particularly useful for applications involving reaction of the pectin with polyvalent cations such as calcium.